MacCREADY THEORY WITH UNCERTAIN LIFT AND LIMITED ALTITUDE

Abstract

Given a MacCready ring setting, every textbook tells you how to fly. Take thermals greater than this setting, leave thermals when they get below the MacCready setting, and adapt to lift and sink via the usual MacCready rules. Much of the mystery, challenge and art of cross-country thermal flying comes down to a judgement what that setting should be. Of course, if we knew the strength of the next thermal, that would be the MacCready setting. But what setting should you use, given the fact that the strength and position of thermals is uncertain, and you may not have enough altitude to reach them before running into the ground? This paper presents a mathematical solution to this long-outstanding problem.  Unsurprisingly, the results describe philosophies already advocated by noted contest pilots, as pilots already had figured out to fly faster on strong days and in sink before MacCready.